Automatic closing of air pipes. DN 300 Automatic closing of air pipes. DN 400 Automatic Closing of Air Pipes . DN 550 Automatic closing of air pipes. DN 600 Automatic closing of air pipes. DN 600 Automatic closing of air pipes. DN 50 Automatic closing of air pipes. DN 350 Automatic closing of air pipes. DN 80 Automatic closing of air pipes. DN 25 Automatic Closing of Air Pipes . DN 50 Automatic closing of air pipes. DN 100 Automatic closing of air pipes. DN 25 Automatic Closing of Air Pipes . DN 350 Automatic Closing of Air Pipes . DN 450 Automatic closing of air pipes. Du350